1. Technical Field
Example embodiments relate to organic memory devices incorporating an electrically conductive organic material containing heteroatoms and methods for fabricating such devices. More specifically, example embodiments relate to organic memory devices comprising a first electrode, a second electrode and an organic active layer sandwiched therebetween, wherein the organic active layer is formed using an electrically conductive organic material containing heteroatoms, and methods for fabricating such organic memory devices.
2. Description of the Related Art
With the recent dramatic developments in digital communication technology, demand for a variety of memory devices has been increasing rapidly. In particular, non-volatile memory devices suitable for use in applications including, for example, mobile terminals, smart cards, electronic money, digital cameras, game memories, MP3 players, and others, are required for retaining data in memory even when no power is being applied to the memory device, thereby tending to reduce the memory-related power consumption of the device.
Perhaps the most common nonvolatile memories currently being utilized in such applications are flash memories based on silicon materials. Conventional flash memories, however, have inherent technical limitations in that the number of writing/erasing cycles is limited, the writing speed is relatively slow, the production costs of memory chips are increased as a result of the complicated processing currently required for attaining sufficiently high memory densities and certain physical limitations that impede further efforts toward miniaturization. In view of these known limitations of conventional flash memories and the processes for fabricating such devices, efforts have continued toward developing next-generation nonvolatile memory devices that can overcome at least certain of the limitations associated with conventional silicon memory devices and provide one or more advantages over the conventional devices including, for example, increased operating speeds, increased density and/or capacity, reduced power consumption and/or reduced production costs.
Some of these next-generation nonvolatile memories may be generally categorized as, for example, ferroelectric RAMs, magnetic RAMs, phase change RAMs, nanotube memories, holographic memories, organic memories, and/or other groupings that tend to reflect the particular constituent materials used in forming the primary memory cells and/or the particular configuration of the materials and/or structures within the memory cells utilized in the semiconductor memory devices. Organic memories, for example, typically include an upper electrode, a lower electrode and a memory layer formed from an organic material positioned between the upper and lower electrodes to utilize the bistability of resistance values obtained when a voltage is applied between the upper and lower electrodes for storing data.
As utilized in organic memories, these bistability resistance characteristics are exhibited by memory cells formed at the intersections or interfaces between the upper and lower electrodes. Accordingly, these organic memories allow the resistance of the organic material positioned between the upper and lower electrodes to be varied repeatedly between higher and lower values through application of appropriate voltage potentials so that data, i.e., ‘0’ and ‘1’, can be written to and read from a single cell. Such organic memories have attracted increasing attention in recent years as next-generation memories because they provide the desired non-volatility, which is an advantage associated with conventional flash memories, while also providing improved processability, reducing fabrication costs and/or improving the degree of integration.
One example of such an organic memory utilizes a 7,7,8,8-tetracyano-p-quinodimethane (CuTCNQ), which is an organometallic charge transfer complex compound, as the organic material. Another example includes semiconductor devices comprising an upper electrode, a lower electrode and an intermediate layer sandwiched therebetween wherein the intermediate layer is formed from a mixture of an ionic salt, for example, NaCl or CsCl, and a conductive polymer. Other work has suggested organic memory devices comprising organic active layers and a metal nanocluster applied between the organic active layers, but efforts in this area have been hampered by low yields, difficulties in forming suitable metal nanoclusters, and reset voltages of about 0 V, rendering such devices generally unsuitable for widespread use as a nonvolatile organic memory.
Metal filament memories are currently being investigated as an alternative memory structure in which the resistance values may be varied by the formation and dissolution, attenuation or removal of metal filaments within an organic active layer sandwiched between two electrodes. The advantages associated with such metal filament memories may include, for example, reduced fabrication costs, the potential for forming three-dimensional stacking structures, increased retention lime, improved thermal stability and/or increased compatibility with flexible substrates. For example, polystyrene films formed from styrene vapor by a glow discharge polymerization technique have shown memory characteristics associated with the formation of metal filaments. However, the formation of metal filaments within polystyrene films have not been demonstrated using more conventional coating techniques, for example, spin coating or spin casting. On the other hand, nonvolatile memory characteristics have been achieved in a metal filament memory device comprising an upper copper electrode, a lower copper electrode and an organic layer formed of a material selected from 2-amino-4,5-imidazoledicarbonitrile (AIDCN), tris-8-(hydroxyquinoline) aluminum (Alq3) and zinc 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (ZnPC). In each of these metal filament memories, however, the organic active layers are formed using vacuum evaporation and thereby requiring complicated fabrication processing and tending to increase fabrication costs relative to other conventional methods of forming organic layers, e.g., spin-coating.